How does EFF's Dice work?

EFF's dice passphrase works by throwing a dice 5 times (or 5 dices at the same time) to generate a 5 digits number (from 11111 to 66666).
That number is then mapped to a preprepared word list (such as this one) and produces one word.

Repeating this process 6 times produces 6 words which combined generates a passphrase of about 2⁷⁷ (that's 221073919720733357899776) alternatives. Quite a lot indeed.